There are nearly 6000 leaks from natural gas pipelines underneath the public road system in Washington DC, some of them at levels far greater than the explosion threshold. These are the critical findings of a team of researchers from the USA who travelled every mile of the 1500 miles of roads in 2013, measuring methane concentrations with a portable cavity ring-down spectrometer. Natural gas was confirmed as the source of methane from the isotopic signatures of methane and ethane.

Writing in Environmental Science and Technology, senior reporter Robert Jackson told how more than 1122 leaks were >5 ppm methane, compared with the background level of 2 ppm. At sites where the concentrations were high, the team stopped to measure levels beneath manhole covers and found that 12 sites contained potentially explosive concentrations ranging from 50,000 to 500,000 ppm. The team notified the gas supply company of the large leaks but 3 months later the majority of them continued to leak at a high rate.

It is likely that the leaks emanate from old cast iron gas pipes that remain in place in the DC gas network. The research team argued that financial incentives to fix the leaks or replace old piping would save billions of dollars in lost gas, as well as making the district a safer place to live and work.

It would be interesting to extend this study to other cities in country, to assess the current risk from leaky pipes.